Various types of biometric systems are used more and more in order to provide for increased security for accessing an electronic device, thereby providing an enhanced user convenience. In particular fingerprint sensors have been successfully integrated in such devices, for example, thanks to their small form factor, high performance and user acceptance. Among the various available fingerprint sensing principles (such as capacitive, optical, thermal etc.), capacitive sensing is most commonly used, in particular in applications where size and power consumption are important issues.
All capacitive fingerprint sensors provide a measure indicative of the capacitance between several sensing elements and a finger placed on the surface of the fingerprint sensor. Acquisition of a partial fingerprint image may be performed using a fingerprint sensor comprising a plurality of sensing elements arranged in a two-dimensional manner, where this fingerprint sensor is configured to in a single image capture the majority of a person's complete fingerprint.
As an alternative, a line sensor may be used for acquiring a fingerprint image, sometimes also referred to as a swipe sensor. The line sensor is typically a thin, rectangular shaped device configured to obtain a plurality of small overlapping images, or snapshots, as a finger is swiped past the sensor. A complete fingerprint image is obtaining by processing these snapshots to form a composite image. The compiling of the smaller images into a complete fingerprint is typically referred to as “stitching” the images.
Successful stitching for forming the complete fingerprint requires extensive computing resources and the collection of a large plurality of overlapping images. Powerful microprocessors, significant amounts of memory, and a relatively long processing time are required to adequately process the fingerprints.
An exemplary implementation trying to improve this fallback is disclosed in US 2007/0274575. Specifically, US 2007/0274575 discloses a method and system for reconstructing seamless fingerprint image from set of image slices, or frames, from a fingerprint swipe sensor. According to US 2007/0274575, minutiae extraction may be performed separately over a sub-portion rather than over the full or complete fingerprint.
Even though US 2007/0274575 introduces an interesting approach to fingerprint feature extraction from portions of a complete fingerprint, the disclosed approach is highly dependent on the overlap of image slices acquired using the fingerprint sensor, resulting in a less than robust system. Thus, there appears to be room for further improvement in regards to efficient and robust processing of fingerprints, specifically in relation to fingerprints collected when a user swipes his/her finger over the fingerprint sensor.